Railway traffic controlling apparatus



Feb. 2 3, 1943. i w p, PLACE v 2,312,050

RAILWAY TRAFFIC coNTRoLLNG-APPARATUS Filed Nov. a, 1941 l Fig. 2.

HIS Arma/vnf.

Patented Feb. 23, 1943 RAILWAY TRAFFIC CONT-ROLLING APPARATUS Willard P. Place, Wilkinsburg, Pa., assignor. to.

The Union Switch & Signal Company, Swiss,- vale, Pa., a corporation of Pennsylvania Application November 8', 1941, Serial No. 418,353

9 Claims.

My invention relates to. railway tramo controlling apparatus', and more particularly toy train` carried train control apparatus responsive to coded energy.

Generally speaking, the codedv current used. to govern present day train carried train control apparatus is supplied across the track rails of a track section at the exit end of the section so that when atrain occupies the section, current flows along one rail, through the wheels and axles of the train andv back the other rail, such current flowing in opposite directions in the rails at any given instant. Inductors are mounted on the train aheadV of the leading pair of wheels with one iuductor over each rail tov inductively pick: up anv electromotive force in response to such coded rail current. Inl many cases the two inductors are connected together in such manner that the electromotive forces induced therein due to current flowing inopposite directions inthe rails addtheir effects andthe resultant electromotive force is applied to the input side ofY a train carried amplifier for operating a code following relay.A connected to the output side of the amplifier. The code fol'- lowing relay in. turn governs decoding means selectively responsive tothe ratel at which the relay is operated. and in turn selectively responsive to the code rate of the rail current. In, some cases the two train carried inductors.. are connected to separate amplifiers and the two electromotiveforces pickedi up. by the inductors are amplified separately. In such case, .the output sidesN of the separate ampliers are con-- nected in such a manner that the outputs are combined for operating the code following relay.

It is the practice to use alternating. current of the order of 100 cycles per second and to code such current by periodically interrupting the circuit at diierent rates, such as` 189, 120 and 75- times per minute. At least such code rates'are those generally used to reflect clear, approachmedium and approach traic conditions, respectively.

The length. or the track. section is predetermined in part according to the desired-spacing of trains andv according to the braking distance required for the trains. operating over'the.- section. The braking distance required4 depends uponY the. maximum permissible speed; and the nature ci! equipment, such. as passenger' or freight cars. The high speedsy prescribedV for present day traiic in loothV freight and-passenger train service requirev relativelylong braking distances and hence a. relatively: long track section if a trainis to be broughtfrom maximum speed to a stop in a single track. section. For this reason track sections of the order of 11,000 feet in length are. provided Where, high train speeds prevail; Broken rail protection is also an essentialn feature in. such railway signaling systems. Asingle track circuit for a track section of 11,000; feet may not provide satisfactory broken rail protection when alternating current of cycles persecond is used. Consequently such 11,000` foot tracksection; may require that it be provided-with oner or more cut section locations to divide the section into subsections, each of which includes; a track circuit. Such cut section locations add to the apparatus. re-

quiredand correspondingly increase the cost.

It has been proposedV to use railwayV trafc controlli-ng apparatus responsiveto coded direct current because direct current will provide satisfactory broken rail protection forlany length of track sectionwithin the limits here contemplated; In order to conservethe output required from the track battery that servesl as the source of the coded directl current; and to provide track circuits of highshunting sensitivity, it has also been proposed to code the direct current in such a manner that a single impulse ofv current of relatively high peak voltage and` short duration is supplied to the railsat the start of each on code period. When v the aforementioned code rates of 180, and- 'limpulses per minute are used with such coding, then the current impulse is'short asA com-pared withthe duration-between successive impulses. For example, the duration of a current impulse may. be of the-order of .05

second and hence under the code rate the duration between successive impulses is about .28 second. Under the other code ratesof 120 and 75; the durationy oi the impulse` wouldv be the same and the duration between successive impulses would bev correspondingly greater. Such code-impulses ci. direct. current cause the code following relay to be. operated with unequal on-andoii. periods unless some additional means is. provided. toV prolong. the effect. oi each code impulse. Thatis, some. meansi'or equalizing. the on and oi periods cf the code following relay is desirable because the standard formv of decoding means governed. by the code following-relay is most satisfactorily operated when thecode followingrelay is operated at substantially. equal onand. off periods. In the present. day arrangement, the code followingrelay governs the decoding means by governing the supply of direct current to a decoding transformer, direct current being alternately supplied to preselected portions of a primary winding of the transformer over normal and reverse contacts of the relay so that when the relay is operated to alternately open and close its contacts current is alternately supplied to the two portions of the primary winding and there is created in a secondary winding of the transformer an alternating electromotive force of a frequency corresponding to the code rate at which the relay is operating and of course, in turn, according to the code rate of the rail current. Consequently, as set forth hereinbefore, it is desirable to provide some equalizing means for equalizing the on and off periods of the relay. Again rigid requirements are placed upon a code following relay having mechanical moving parts because such code following relay is in continuous opera'- tion,

When coded direct current is used operating diniculties may be experienced because of the possible false energization of the .train carried amplifier produced by the so-called magnetized spots of the track rails. Such magnetized spots occur at random and act to induce an electromotive force in a train carried inductor as the train moves over such rail spot. Such stray electromotive force when amplified may adversely affect the operation of the code vfollowing relay.

In view of these various conditions imposed upon railway traffic controlling apparatus of the type here involved, a feature of my invention is the provision of a novel and improved organization of railway traffic controlling apparatus responsive to coded direct current.

Another feature of my invention is the provision of train carried train control apparatus incorporating novel and improved receiving and amplifying means wherewth such amplifying means is effectively excited only when two elec-A tromotive forces are simultaneously picked up one from each rail and when such electromotive forces are of a predetermined phase relation, and electromotive forces created by random magnetic fields do not effectively excite the amplifier.

Again, a feature of my invention is the provision of railway traffic controlling apparatus of the type here contemplated incorporating novel means for equalizing the resultant on and ofi periods of a code following relay governed by energy impulses of short duration as compared to the duration between successive impulses.

Another feature of my invention is the provision of train carried .train control apparatus which is free from mechanical moving parts. y

Furthermore, a feature of my invention is the provision of railway traffic controlling apparatus of the type here involved incorporating novel means for alternately firing two gas filled tubes for substantially equal periods in 'response to coded direct current and which means automatically varies the firing period according to the code rate of the current and which tubes are adaptable of functioning as a code following relay of no moving parts for controlling decoding means selectively responsive ,to different predetermined codevrates. n

Other features, objects and advantages of my invention will appear as the specification prov gresses.

The above features, advantages and objects of my invention are obtained by providing on a train Y adapted tovtravel a ,track section whose rails are supplied with direct current coded at different code rates, a receiving and amplifying means, an

' each such tube.

equalizing relay means and the usual standard decoding and signaling means. The receiving and amplifying means comprises two inductorc mounted on the train in advance of the leading pair of wheels with one inductor over each rail, and a multiple tube two channel amplifier. The two electromotive forces rinduced in the two inductors by each on period or code impulse of rail current are applied one to each of two tubes of the amplifier with the result an enlarged electromotive force of a code corresponding to the code of the rail current appears in the output of The output electromotive force of one of these two tubes is applied to the grid of OSL a third tube of the amplifier and the output electromotive force of the other one of the first mentioned two tubes of the amplifier is applied to the plate circuit of the third tube, the arrangement tubes appear simultaneously and are in phase with each other. Thus a current impulse in the output of the third tube of the amplifier can happen only when the coded rail current flows in the two rails in opposite directions at the same instant, and stray magnetic fields which excite one inductor only or which excite both inductors but at dfferent times or which excite both inductors at the same time but do not create electromotive forces of a proper phase relation do not cause an effective current impulse to appear in the output of the third tube of the amplifier.

The equalizing relay means comprises two gas lled or controlled ionization type of electron Y anode circuits is of a voltage suicient to fire each tube when the grid of a tube is of substantially zero potential with respect to the tube cathode.

' The grid circuit of a first one fof the gas filled tubes includes a voltage source, such as a battery, to effect a negative grid bias voltage so'that this first gas filled tube is normally extinguished. The grid circuit for this first gas filled tube also includes a winding which is coupled to the output of the third tube of the receiving amplifier, and each current impulse caused to fiow in the output of the receiving amplifier sets up an electromotive force in the grid circuit of the first gas filled tube that overcomes the normal grid bias voltage due to the battery and this first gas lled tube is fired. In otherwords, a first one of the gas filled tubes is normally biased to be extinguished and is fired in response to each on period of the rail current. The grid circuit for the second gas filled tube includes no normally active source of negative bias voltage and the tube is normally fired due to the Voltage of the current source of the anode circuit. The grid circuit of the second tube is provided, however, with a biasing means including resistors and condensers, such condensers becoming Acharged due to the voltage drop across the associated resistors 'as caused by the normal flow of anode current. The arrange- `ment of this biasing means is such that when the second gas filled tube becomes extinguished, the charge on the condensers produces a negative grid blas voltage that prevents this second tube from 1 becoming refired bythe anode current sourceu'ntil the charge on the' condensers leaks off through the associated resistors. ond gas lled tube is. normally red, but once extinguished it remains extinguishedfor an interval whose duration is predetermined by the charge built up on the associated biasing means. An extinguishing reactance, preferably in the form of? a condenser, is connected to the anode circuits of' the two gas lledtubes to alternately extinguish the tubes. To sum up, therefore, the rst gas filled tube is normally extinguished and the second gas lled tubeis normally fired, the rst tube is fired in response to an electromotive force created by the coded rail current, theA second tube is extinguished by the extinguishing condenser immediately following the firing of the first tube, the secondV tube is rered after a predetermined interval as determined by the charge on its biasingk means, and the first tube'is extinguished by the extinguishing condenser immediately following the rering Iof the second tube, the two gas filled tubes being then ready to-repeat this cycle of operation at the next electromotive force created by the coded rail current. It is to be understood of course that the second tube is refired during the duration between successive electromotive forces. Since the anode circuit of each of the gas filled tubes includes a preselected portion of a primary winding of the decoding transformer, such alternate firing of the gaslled tubes causes direct current to alternately flow in the two portions of the primary winding of the decoding transformer and an alternating electromotive force is induced in a secondary winding of such transformer, the frequency of such alternating electromotive force corresponding tothe rate at which the two gas filled tubes are alternately red, and in turn according to the code rate of the rail current.

The. decoding means comprises tuned decoding cricuits of the usual standard form and which circuits are connected directly to the secondary winding of the decoding transformer. The decoding circuits govern a cab signal or other train control devices according tothe frequency of the electromotive forces applied to such circuits.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In. the accompanying drawing, Fig. l is a diagrammatic view showing oner form of apparatus embodying my invention when used with train carried train control apparatus. Fig. 2 is a diagram illustrating an operating characteristic of the apparatus of Fig. l.

Referring to Fig. 1, the reference characters la, and Ib designate the track rails of a stretch of railway over which traflic normally moves in the direction indicated by an arrow, and which rails are formed by the usual insulated rail joints into a track section D-E, which section may be one section of a series of consecutive sections of a signalV system. The track section D-E is provided with a track circuit comprising a source of codedr current connected across the rails at the exit end of the section and a code following relay connected across the rails at the entrance end of the section. In the present embodiment of my invention, use of code impulses of direct current is contemplated and theV source of coded direct current for the track circuit of section D-E comprises a battery 1, a code transmitter or coder CT and a track transformer lor reactor TD. Secondary winding 2 of transformer TD is connected across the rails at exit end D over wires 3 and 4.

In other Words, the sec-` Primary winding 6v of transformer TD is con- 75 nected to battery 'l over either codecontact member 15.` or of coder-CT' according to theposition of a traic controlled relay HD. A condenser 8 is. preferably connected across primary i winding 6.

Code transmitter CT may take the` form, ofY

any one of several well-known structures for such devices and itis sufcient to point out; that as long as its operating windinggzis supplied with current from any convenient source of current, notshown, the code contact members 'i5 and |86 areoperated at preselected, codev rates. For example, contact member l5 is` operated to engage land disengagey a contact- 15a at the rate of 75 times per minute and contact. member |891 is operated to engage and disengage a contact I'Ba at the rate of times. per minute. The relay HD is controlledY by trafficy conditions in advance of section D-E, but such control apparatusis not shown since it would be in: accordance with standard practice and forms no part of my present invention. It is suflicient for the present application topoint. out that relay HD is picked up to close front contact Hl, when the` section next in advance of section D-E is unoccupied,

and the relay is released closing back .contact when such section next. in advance is occupied. In other words, relay Hl).v is picked up underl clear traffic conditions in advance and' is; released under approach traic conditions. in advance. When relay HD is picked up closing front contact l0, battery 'I is connected, to.'k primary winding 6 over a circuit including code contact member |80 of coder CT, vand duringeach interval, that con- I tact I-la is closed direct current flows in winding 5 causing magnetic energy to be stored in the magnetic core of transformer TD. The circuit including battery l', front contact |0 and primary winding 6. is so proportioned as` to its time constant that the magnetic energy builds up relatively slow and little, if any, electromotive force is induced in secondary winding 2, at least such electromotive force is so. small it can be neglected. When. contact member |80. breaks engagement with contact I'Ba, the flow of current from battery 1 iszinterrupted. andthe magnetic energy stored in transformer TD decays rapidly and an electromotive force of relatively high peak voltage is induced'in secondary Winding 2 and a current impulse of relatively high peak voltage is supplied' to the track rails: of section D-E. This impulse of directcurrent is of a given polarity and is of short duration, the part being proportioned to provide an impulse of current of the order of say .05 second. Consequently, a code impulse offcurrent is suppliedV to the rails each operation of code-contact member l and direct current of the. code rate of 180 impulses per minute is supplied to the railsv as long as relay HD is picked up'. That is, such code rate of direct current is` supplied to the rails under clear traffic conditions. Under approach trafc conditions, relay HD is released closing back contact. H, and' batteryY l is connected to primary winding 6.. over contact mem-` ber 15 and the operation. is the same as described above except that current ofthe codev rate of '75 impulses per minute is supplied to the track rails. It is to be observed that under each code rate the duration of the current impulse, here assumed as .05 second, is short as compared to the duration between successive impulses, the duration between the impulses of the 180 code rate being substantially- .28V second, and.- being substantially .'75 second under the-'75 code rate.

It will be understood, of course, that my invention is not limited to code rates of 75 and 180 impulses per minute or to impulses of the duration of .05 second, but such code rates and characteristics for the direct current impulses have been found satisfactory. As a matter of fact, the direct current for the track circuit'of section D-E may be coded to provide substantially equal on and off periods for the current.

A code following track relay CF is connected across the rails at entrance end E, and when section D-E is unoccupied, that is, when a train shown conventionally at TV does not occupy the section, relay CF is operated at Aa code rate corresponding to the code rate of the current impulses supplied to the rails through transformer TD in the manner just explained. Track relay CF would be used to govern apparatus including a control relay for the section next in the rear of section D-E and which relay would be similar to control relay HD governed by traffic in advance of section D-E. The apparatus governed by track relay CF is not shown for the sake of simplicity because such apparatus forms no part of my invention and would be in accordance with standard practice.

The train shown conventionally at TV is provided with train carried train control apparatus embodying my invention, and which apparatus comprises a receiving and amplifying means to be shortly described, an equalizing relay means including two gas lled tubes GI and G2 and a novel circuit arrangement, a decoding transformer DT, decoding circuits DM, control relays A and L and a cab signal CS, together with the necessary sources of current.

The receiving and amplifying means comprises inductors I2 and I3 and three amplifying electron tubes VTI, VT2 and VT3, together with the necessary circuits. Inductors I2 and I3 are preferably alike and are mounted on the train ahead of the leading pair of wheels and in in ductive relation to the rails Ia and Ib, respectively. It follows that when train TV occupies section D-E and there is no other train between it vand the exit end of the section, an electromotive force is picked up by each inductor I2 and I3 in response to each code impulse or on period of the direct current supplied to the rails of the section through track transformer TD, each such picked up electromotive force having a code rate characteristic corresponding to the coded rail current. This is so because such cur rent flows along say, rail Ia, through the train shunt 'andback rail Ib.

Inductors I2 and I3 are connected to the input side of tubes VTI and VT2, respectively, which as here shown are of the indirect heater type. To be explicit, inductor I2 is connected to primary winding I1 of a transformer TI over wires I4 and I5, a condenser I6 being interposed in wire I4; and a condenser I8 is connected across secondary winding I9 of transformer TI, and secondary winding I9 and condenser I8 in multiple are connected across grid and cathode 2| of tube VTI, a biasing battery 22 being interposed in the connection to provide a desirable grid bias voltage for the tube. Similarly, inductor I3 is connected to primary winding 23 of a transformer T2 over wires 24 and 25, a condenser 26 being interposed in wire 25; and a condenser 21 is connected across secondary winding 28 of transformer T2, and secondary winding 28 and condenser 21 in multiple are connected vacross grid 29 and cathode 30 of tube VT2, a battery 3| using the code impulses of electromotive force created in secondary Winding will be 4die being interposed in theconnection t0 provide a desired grid bias voltage for tube VT2.

The rst tube VTI has a plate circuit that includes a direct current source whose terminals are indicated at B300 and N300, and a primary winding 32 of a transformer T3; While the second tube VT2 has a plate circuit that includes the B300-N300current source and a primary winding 33 of a transformer T4. The filaments of tubes VTI and VT2 are heated in the usual manner by a current source, not shown, and it f ollows that the two electromotive forces induced in inductors I2 and I3 by a code impulse of rail current are applied simultaneously to the respective tubes VTI and VT2, and correspondingly enlarged electromotive forces appear in the secondary windings 34 vand 35 of transformers T3 and T4, these two latter electromotive forces being of like character and of a phase relation predetermined by the connection of inductors yI2 and I3 and associatedV transformers. Furthermore, the electromotive forces created in secondaryY windings 34 and 3 5 are of the-,same code rate as the rail current. To aid in the understanding of the apparatus, it is to be noted that the connections are such that the effective electromotive forces induced in secondary windings 34 and 35 cause in each case the top terminal of the associated winding to be positive and the bottom terminal to be negative, as indi` cated by the plus and minus signs placed onthe drawing. c

The third tube VT3 of the amplifier is also shown as of the indirect heater type whose filament is normally heated in the usual manner.

The secondary winding'34 of transformer T3 is connected across grid 36 and cathode 31 of tube VT3, and secondary winding 35 ofA transformer T4 is connected across plate 38 and cathode 31 of tube VT3. A primary Winding 39 of an out-Y put transformer T5 is included in the plate circuit of tube VT3. Hence, the electromotive force picked up by inductor I2 and amplified by the tube VTI causes a corresponding electromotive Y force to be applied to the grid of tube VT3, and

the electromotiver force picked up by inductor I3 and amplified by tube jVT2 causes a corre-A spending electromotive force to be applied to the plate circuit of tube VT3. lWhen these two elec- 'tromotive forces applied to the plateand grid circuits of tube'VT3 occur so that the grid'is driven` more positive in potential with respect to cathode 31 at the same instant plate 38 is positive, current flows in the plate circuit of tube -VT3 and an electromotive force is induced in secondary winding 40 of output transformer T5. It is clear that if these two electromotive forces applied to tube VT3 are out of phase or only one occurs at a time, or are of the polarity opposite to that shown in Fig. 1, no electromotive force appears in the secondary winding .40 of output transformer T5. Consequently the coded direct current applied to the rails of section D-E is effective to create an electromotive force of `acorresponding code rate in the secondary winding 40 of the output transformer T5, but stray magnetic fields that excite a single inductor at a time or excite the two inductors out of phase are ineffective to create'an electromotive force' in the 'output of the'amplier. The manner of scribed hereinafter.` Y

A The gas filledgor controlled ionization tubes G and G2 -of theV relay equalizing means 'are'y shown as of the .indirect heater type whoselaments would ibe continuously heated linthe usual manner, These tubes Gl and G2 are provided with anode circuits, each of which includes the B300- N350 current source Vand a preselected portion of apr'imary winding 4| :of 'decoding transformer DT. That is, the anode circuit of the rst tube GI can be traced vfrom terminal B305 over wire 42 to 'a center terminal :of primary winding v4| of transformer DT, top half portion of Winding 4| as viewed'in Fig. Il, anode 430i tube Gl, intervening tube space `t cathode 44, and wire `45 to terminal N350; and the anode circuit for tube YG2 includes terminal B390, Wire 42, lower half portion rof primary winding 4|, anode d5 of tube G2, intervening tube space to cathode 4l, a biasing unit BU to be referred to later, and wire 45 to terminal N309. The voltage of the B305- N current source is high 'enough to "nre tubes G| and G2 when the grid of 'a tubeis of substantially the same potential as the cathode 'of the tube.

The grid circuit for .the first tube Gi includes grid 4S, resistor '49, winding 4|)` 'of transformer T5, a battery 5i! and cathode 44. Battery z5! is selected and ldisposed so as to provide a negative grid Vbias voltage 'suicient that tube G'| is normally retained extinguished. The connections'of secondary winding 45 of transformer T5 are such that 'the 'electromotive force produced therein in response to the coded rail .current, .as explained hereinbefore, overcomes the voltage of battery '50 and tube Gl is `red, due to the voltage of the BBl-NSB current source. That is, tube G'I yis normally retained extinguished or non-conductive and is Viired and becomes conductive inresponse to Veach electromotive force created in winding 40 dueto the rail current. Once iired, tube G| remains in 'that condition subsequentJ .to the termination of the electromotive force created in winding 45 until the tube is extinguished .in a manner to shortly appear.

The grid circuit for the second gas lled tube G2 includes grid 15|, grid Yleak 'resistor R1, biasing unit BU and cathode 4l. 'The unit BU comprises a condenser C2 'and a resistor `R2 in multiple. Also a condenser C| yis 'connected loetween grid 5| and the anode 43 of the rst'tube Gi. Since there is no normally active 'source of voltage in the grid circuit 'of tube G2, the tube is normally fired due to the voltage impressed across .its anode and cathode by the BINS-N305 current source. The anode current of tube G2 flowing through the lower half portion of primary winding 4| of transformer DT and through resistor R2 of unit BU causes Acondenser C2 of unit BU to be 'charged ata potential substantially equal 'to the voltage drop across resistor R2, and condenser C| to be charged at a potential substantially equal to the voltage drop through the lower half portion of primary winding 4l. It is clear that once tube G2 is extinguished the grid 5| is rendered negative in potential with respect to the cathode 41 by the charge on either or both condensers C2 and Ci. When tube G2 is extinguished the charge on condenser C2 is discharged through resistor R2. The charge on condenser CI can be discharged through a path comprising resistor RI and the tube Gi when that tube is red and made of low resistance. After a time interval, predetermined by the proportioning oi the parts, condensers C| and C2 become discharged and the negative grid bias voltage of grid 5| is revduced to apoint where the tube G2 is reiired due to the voltage of the BMU-N360 current source.

An extinguishing reactance here shown as a condenser C3 is connected across theoutside terminals of primary winding 4| of transformer DT, that is, condenser C3 is connected across 'the anodes oi tubes GI and G2. With tube G2 normally Yconductive and tube Gi normally nonconductive, condenser C3 is charged to a potentia-l'substantially -equalfto the voltage drop across the lower fha-lf portion of primary winding 4|, the top terminal of condenser C3 rbeing positi-ve vWith `respect to its lower terminal. If tube AG-| -is now :fired vthe charge 'of condenser C3 is applied across cathode 41 and anode "46 oftube G2 to'eXting-uish tube G2. I-t is to be noted` that condenser \C| is charged Vat a polarity Ythatvits discharge vaids in lextinguishing tube G2. When tube GI is conductive, condenser C3 -is charged due to the voltage drop through lthe top half portion of primary winding 4|, the -lower terkmin-al of condenser C3 Ybeing positive with `respect to its top terminal. If tube G2 .is now fired, 'the Acharge on condenser C3 is applied across cathode 44 and anode 443 fof tube yG| to extinguish -tube Gl.

It is -to be seen, therefore, that when a ycede impulse oi eleotromotive force appears -in `secondary winding 40 of the output ofthe receiving amplien tube GI is fired, tube 'G2 is immediately extinguished due to condenser C3 and remains extinguished until -condensers -CZ and C| lare :discharged through `the vassociated resistors. Tube G2 -is `then refired and tube GI is extinguished due to. Ycondenser C3. This alternate firing -of tubes Grl -and 'G2 is lrepeated for weach code impulse 'of electromotive force appearing in -secondary winding 40, vit being understood of course that the condensers C2 and 'C-| ydischarge to permit tube G2 to be reflr-ed lduring the interval between successive impulses-of the electromotive forces.

'Theanode currents for vtubes GI and G2 flow in the two'half portions of primary winding 4| .of transformer `Dll alternately and Mhence cause yan alternatingelectromotive force tobe induced in secondary winding 52 of that transformer, the .frequency 'of such alternating -electromotive -force corresponding to the rate at which the two tubes are alternately fired.

Secondary Winding -52 of ltransformer DT is connected to decoding circuits DM which preferably consist of the rstandard -form of tuned decoding circuits. -A first one of -such decoding .circuits includes a condenser v53 and an inductor 54, across at least a portion -of which ind-uctor control relay A is connected through a full wave -rec'tier 55. A second decoding `circuit includes an inductor 56 across at least a portion of which.l is connected control `relay L through `a `full wave rectier 5l. The nrs-t mentioned decoding circuit vis tuned to resonance at the vfrequency of the alternating electromotive vforce created in secondary winding 52 in response t'othe 1`80 'code rate of the rail current. The second mentioned decoding `circuitl is nonetune'cl. Consequently vcontrol relay -A is Yeffectively energized and picked up only -in respense 'to Trail current of 180 code rate and relay L is effectively Aenergized `and picked Vup .in response to rail 'current 'or either 'the "l5 or 180 code rate. Both relays 'A and TL are 'released when no electrornotive force is produced in secondary winding 52.

Control relays A and L are used vto vvgovern the operating circuits of suitable train carriedy train control devices such as cab signal CS operable to display any one of three different signal indications. As here shown, when relay A is picked up to close front contact 58 a circuit is formed for a green light G and signal CS displays a green light for a clear signal indication; when relay A Ais released and relay L is picked up, a circuit is formed over back Contact 59 of relay A, front contact 60 of relay L, and yellow lamp Y of signal CS'and signal CS displays a yellow light for an approach signal indication; and when both relays A and L are released closing back contacts 59 and 6l, respectively, a circuit is formed for a red lamp R of signal CS and signal CS displays a Ired light for a slow speed signal indication.

In describing the operation of the apparatus I shall rst assume that train TV occupies section D-E at a time when relay HD is picked up in response to clear traffic conditions in advance and code impulses of current of the 180 code rate vare supplied to the rails of section D-E. At the start, a rst code impulse of rail current induces electromotive forces in inductors I2 and I3 which are amplified by tubes VTI and VTZ, respectively,

and there appears a corresponding4 impulse of electromotive force in secondary winding'llll of transformer T in the output of tube VTS. This latter electromotive force created in secondary winding 40 of transformer T5 causes tube GI` to be fired and with tube Gl fired, the normally fired tube G2 is immediately extinguished due to condenser C3. Tube GI remains fired and tube G2 remains extinguished subsequent to the termination of the electromotive force created in\ ing electromotive force of a frequency corresponding to the 180 code rate of rail current. The control relay A is now picked up and the cab signal CS is operated to display a green light as a clear signal indication. The biasing means associated with tube G2 is so proportioned and adjusted that tubes GI and G2 are alternatelynred at substantially equal periods, and the e1ectromotive force induced in secondary windingl 52 of decoding transformer DT and applied to the decoding circuits has substantially equal half cycle periods. l Y

I shall next assume that the train TV occupies the'section D-E at a time whencontrol relay HD is released due to approach traffic conditions in advance and direct current of ythe code rate is supplied to the rails of sectionfD-E The operation of the train carried apparatus is the same as described in connection with current of the 180 Acode rate, except the alternating electromotive force appearing in secondary winding 52 of the decoding transformer and applied to the decoding circuits is of a frequency corresponding to the 75 code rate, and relay A is released and relay L is picked up. i This set-up of control relaysA and L causes signal CS to display a yellow light as an approach signal indication. g

InA the event another train occupies section D--E ahead of train TV, then the coded current supplied to the rails is shunted away from train TV and no electromotive force is picked up by the inductors and no alternating electromotive force is created in secondary winding 52 of the vdecoding transformer with the result relays A .and L are both released and signal CS displays a red light for a slow speed signal indication.

In order to understand how equalized firing time (on and off periods) of the gas filled tubes is accomplished for the different code rates, consider the amount of current that flows through each half portion of the primary winding 4I of decoding transformer DT under the different conditions. If the firing times (on periods) of the two tubes are equal, the magnetic flux set up in transformer DT during the firing of each tube is substantially equal and opposite. Under such circumstances the hysteresis loop of transformer -DT will besymmetrical as illustrated in Fig. 2,

and the decoding transformer operates efficiently, the greater part of the current supplied to its primary winding being useful load current and only a small fraction of the current being used to supply magnetizing losses. If, however, the firing periods of the two tubes GI and G2 are not equal in length, t-he operating point of the magnetic core of transformer DT shifts to a point on the` BH curve where the operation during one period will not be efficient and an excess of magnetizing current is required. This is made use of by arranging the circuit constant of tube G2 so that its tendency is to become red and conductive early. However, if the firing starts too early it will be conducting for a period greater than the conducting period of tube GI and the excess of magnetizing current builds up a larger charge in condenser C2 of the biasing unit of tube G2. Such larger charge von condenser C2 tends to retain tube G2V extinguished a little longer at the next cycle of operation and the tendency Vis for the conducting (on) periods of the two tubes to equalize even if the code rates vary. That is, such variations of lthe magnetization in the code of the decoding transformer tends to vary the charge on the condenser of the biasing unit of tube G2 which in turn tends to cause a substantially equal ring time for the two tubes under the different code rates of the rail current impulses.

Apparatus embodying my invention has the advantage that coded direct current can be used and satisfactory broken rail and high shunting sensitivity provided for a longr track circuit, stray magnetic fields and magnetized rail spots do not adversely excite the receiving amplifier to cause a false operating impulse, equalization of the half cycles of the current supplied to the decoding means is effected for the different code rates by gas filled tubes, the output of which tubes is sufficient to enable standard decoding circuits to be controlled direct from the output of the gas lled tubes and a code following relay having moving parts is avoided.

Although I have herein shown and described only one form of railway traflic controlling apparatus embodying my invention, it is undermeans on the train coupled to the rails to pick up time spaced electromotive forces in response to such coded rail current, two train carried gas lled tubes provided with anode circuits having a common source of direct current and each of which circuits includes a preselected portion of a primary winding of a decoding transformer, said direct current source of a voltage sufficient to normally each of said tubes, a grid circuit including a winding coupled to lsaid receiving means and a source of biasing voltage fora .first one of said tubes, said biasing Voltage source disposed to provide a predetermined negative grid voltage to prevent said first tube from being fired and said winding disposed to overcome such negative grid voltage and permit the rst tube to be nred in response to each said picked up electromotive i'orce, a grid circuit including a biasing unit comprising a resistor and a condenser in multiple for a second one of said tubes, said biasing unit disposed adjacent the cathode of the second tube vto be also included in the anode circuit of the second tube tocharge said condenser while said second tube is fired to provide a negative grid bias voltage for the second tube for a predetermined period when thev second tube is extinguished, means including another condenser connected to said anode circuits toA alternately extinguish said tubes, and signaling means connected to said decoding transformer controlled by the current flowing in said portions of the primary winding due to the alternating nring of said tubes.

2. In combination, a track section, means to supply coded direct current to the rails of the section, a train to travel such section, receiving means on the train lcoupled to the rails to pick up time spaced electromotive forces in response to such coded rail current, a rst and a second train carried gas filled tube, said tubes provided with anode circuits having Aa common source of direct current and each oi which circuits includes a preselected portion oi a primary winding oi a decoding transformer, said direct current source effective to fire each such tube when its grid is of substantially the same potential as its cathode, a grid circuit i'or said rst tube including a battery disposed to provide a negative grid bias Voltage that normally prevents said rstI tube from being fired, a grid circuit for said second tube including a condenser anda resistor in multiple, said resistor disposed adjacent the cathode of the second tube to be also included in the second tube anode circuit to charge said condenser 'while said second tube is normally fired for providing a negative grid bias voltage that retains said second tube extinguished fora pre-A determined period subsequent tothe second -tube being extinguished, means to couple said receiving means to said first tube grid circuit to re the first tube in response to each said electromotive force picked up, extinguishing means including a condenser connected 'to said anode circuits to alternately extinguish said tubes, and signaling means connected to said transformerl eiectively controlled by the currents thus cau-sed to alternately flow in said anode circuits.

3. In combination, a track section, `means to supply coded direct current to'the rails of the section, a train to travel such section, receiving means on the train coupled to the rails to pick up time spaced electromotive forces in response to such coded rail current, a rst and a second train carried gas lled tube, said tubes provided with anode circuitsv having a commonsource offd-irect current of a voltage sufficient to fire the tubes, a

decoding transformer having a d'iierent portion 'of its primary winding interposed in each said vmulti-'ple for said second tube, said unit disposed to be also included in the second tube anode cire cuit to charge said condenser when the second `tube is fired to provide when the second tube is 'extinguished a negative grid bias voltage that prevents reflring of the second tube for an interval preselected to be less than the interval between successive picked up electromotive forces, means including a winding to couple said receiving means `to said iirs't tube grid circuit to fire the rs't tube by each picked up electromotive force, means includ-ing another condenser connected to said anode circuits to alternately extinguish said tubes, and signaling means connected to a secondary winding of said transformer and controlled by the currents thus caused to alternately flow in said portions of the primary winding,

4. In combination, a track section, means to supply to the rails of such section direct current coded t'o have alternate on and ofi' periods, a train to travel the section, receiving means on the train coupled to the rails to pick up time spaced impulses of electromotive force chara'cterizedA by each `impulse being of short duration as compared to the duration between successive impulses Yin response 'to such rcoded rail current, two train carried gas lled tubes, an anode circuit including a direct current source for each said tubes and which direct current source is of a voltage edective to normally fire the tube, a decoding transformer having a different portion of its pri-mary winding interposed in each of said anode circuits, 'a grid circuit including a bias voltage source for a first one of said tubes to normally prevent said `irst tube from being red, means to couple said receiving means to said rst tube grid circuit to fire the first tube in response to each said picked up electromotive force, a grid circuit including a biasing unit comprising a resister and 'a condenser for the second one of said tubes, means including another condenser connected 'to said anode circuits 'to alternately extinguish the tubes, said biasing unit disposed to be' also included in the second tube anode circuit to charge the condenser of the unit when the second tube is fired to create a negative grid bias voltage that effects a predetermined delay in the refiring of the second tube when it is extinguished and causes the tubes to be alternately fired -fr substantially equal periods of time in response to said time spaced electromotive forces, and signaling means connected to a secondary winding of said transformer effectively energized due to such alternating operation of said tubes.

5. In combination, a track section, means to supply to the rails of the section recurrent impulse of direct current each impulse of which is of short duration as compared to the duration between successive impulses, a train to travel the section, receiving means on the train coupled to the rails to pick up an electromotive force in response to each said current impulse, a first and a second train carried gas filled tube provided with ano'de circuits having a common source of direct current and each including a preselected portion of a primary winding of a transformer, said direct current source of a voltage eective to normally nre each of said tubes, a grid circuit for said rst tube including a battery effective to normally prevent that tube from firing and a winding coupled to said receiving means to cause the first tube to be fired in response to each said electromotive force picked up by said receiving means, a grid circuit for said second tube including a biasing unit comprising a condenser and a resistor in multiple and disposed adjacent the tube cathode to be also included in the anode circuit for normally charging said condenser, another condenser connected to said anode circuits to alternately extinguish said tubes, said biasing unit eiective to provide a predetermined delay in the rering of the second tube and cause said tubes to be alternately red for substantially equal periods l of time in response to said recurrent impulses of rail current, and signaling means connected to a secondary winding of said transformer effectively energized due to the alternate owing of current in said anode circuits.

6. In combination, a track section, means to supply time spaced impulses of direct current to the rails of the section, a train to travel such section, receiving means on the train coupled to the rails to pick up an electromotive force in response to each such impulse of rail current, a rst and a second train carried gas filled tube provided with anode circuits having a common source of direct current and each of which circuits includes a preselected portion of a primary winding of a decoding transformer, said direct current source 4eiective to re each such tube when its grid is of substantially the same potential as its cathode, a grid circuit for said rst tube including a battery disposed to provide a v negative grid bias voltage that normally prevents the ring of the rst tube, a grid circuit for said second tube including a resistor, a rst condenser connected between the first tube anode and the grid of the second tube to charge that condenser while the second tube is normally red, a Winding coupled to said receiving means and interposed in said rst tube grid circuit to cause said rst tube to fire in response to each said picked up electromotive force, a second condenser connected to said anode circuits to alternately extinguish said tubes, said rst condenser discharging through said resistor and said rst tube when fired to provide a predetermined delay in the rering of said second tube, and signaling means connected to a secondary winding of said transformer and controlled -by the electromotive force induced in the secondary winding due to the alternating ring of said tubes.

7. In combination, a track section, means to supply time spaced impulses of direct current to `therails of the section, a train to travel such section, receiving means on the train coupled to the rails to pick up an electromotive force in response to each such impulse of rail current, a first and a second train carried gas lled tube provided with anode circuits having a common source of direct current and each of which circuits includes a preselected portion of a primary winding of a decoding transformer, said direct current source effective to nre each such tube when its grid is of substantially the same potential as its cathode, a grid circuit for said first tube including a battery disposed to provide a negative grid bias voltage that normally prevents the firing of that tube, grid circuit means including a biasing unit and a second condenser for said second tube, said unit comprising a rst condenser and a rst resistor in multiple and disposed common to both anode and grid circuits of the said second tube to charge the first condenser when that tube is red, said second condenser connected to the anode of said first tube and grid of said second tube to charge said second condenser when the second tube is fired, a third condenser connected across the anodes of said tubes to alternately extinguish said tubes, a winding coupled to said receiving means and interposed in the rst tube grid circuitl to cause the first tube to be red in response to each said picked up electromotive force, said biasing unit and said second condenser cooperating to provide a negative grid bias voltage for said second tube to provide a preselected delay in the rering of said second tube subsequent to the ring of said first tube and the extinguishing of said second tube, and signaling means connected to a secondary winding of said transformer effectively controlled by the electromotive force induced therein due to current caused to alternately flow in said portions of said primary winding.

8. Railway traffic controlling apparatus comprising, traflic controlled receiving and amplifying means including a control winding and operative to create across said winding time spaced impulses of electromotive force of any one of a plurality of different code rates, two gas filled tubes provided with anode circuits each of which circuits includes a preselected portion of Aa primary winding of a decoding transformer, a direct current source for Isaid anode circuits having a voltage sulicient to re each tube when a tube grid is of the same potential as the tube cathode, a grid circuit of the first one of said tubes including a voltage source to provide a negative grid bias voltage to prevent that tube from normally ring, a grid circuit including a biasing unit for a second one of said tubes, said biasing unit comprising a condenser and a resistor and disposed common to both the grid and anode circuits of such second tube to charge said condenser when the tube is fired and to provide a negative grid bias voltage that permits the rering of said second tube for a preselected period subsequent to that tube being extinguished, another condenser connected across the anodes of said tubes to alternately extinguish the tubes, said control winding interposed in the grid circuit of said rst tube to fire that tube in response to each of said impulses of electromotive force, said biasing unit and decoding transformer proportioned to effect substantially equal ring periods of the two tubes under each of said code rates, and decoding circuits connected to a secondary winding of said transformer and actuated to a distinctive condition in response to the frequency'of the electromotive force induced in such secondary winding due to the different rates at which said tubes are alternately fired.

9. In combination, a track section, means to supply coded direct current to the rails of said section, a train to travel the section, two inductors mounted on the train one above each rail to pick up an electromotive force in response to each code impulse of said direct current, a train carried amplifier tube having its grid coupled to one'of said inductors and its plate coupled to the other one of said 'inductors to create an electromotive force in a Winding linterposed in the plate circuit of said tube only when the inductor electromotive forces occur simultaneously and of a predetermined phase relation, two train carrled gas lled tubes each provided with an anode circuit having a current source of a voltage sufcient to re the tube, a grid circuit including a source of bias voltage and a winding for a first one of said tubes, said bias voltage source of a voltage to normally prevent the ring of the tube and said grid circuit Winding coupled to the rst mentioned winding to cause said first tube to be red by said electromotive force created in said rst mentioned Winding, a

and disposed to charge said condenser when the second tube is fired to provide a negative grid bias voltage for the second tube and provide a predetermined delay in the refiring of the second tube once it is extinguished, another condenser connected to the anode circuits of said gas filled tubes to alternately extinguish the tubes, and signaling means coupled to the anode circuits of the gas lled tubes controlled by the currents grid circuit including a bias unit for a second 10 thus caused to alternately flow therein.

one of said gas filled tubes, said bias unit comprising a condenser and a resistor in multiple WILLARD P. PLACE. 

